On the basis of a pot experiment set up according to the additive design, the effect of competitive actions of spring barley on the morphological characteristics of red clover in the conditions of water stress was evaluated. Biometric analyses were carried out on five dates set by the growth rhythm of barley in pure sowing with a higher water dose. The study included: plant height, number of shoots and leaves per plant, and root length. On the basis of plant biomass, relative yield, relative yield total, and competitive balance index were determined. It was demonstrated that spring barley, from tillering to the end of growth, limited red clover plant height and root length. At the straw-shooting stage, negative effect of the cereal intensified and caused the formation of a smaller number of leaves and shoots than in clover in pure sowing. Water shortage caused plant shortening (from barley tillering to the end of growth) and reduction in the number of leaves (tillering – earing) and shoots (straw-shooting and ripening) of clover.